Field
The described embodiments relate to photonic structures with reduced thermal variation of optical parameters. More specifically, the described embodiments relate to silicon photonic structures with a reduced thermo-optic effect.
Related Art
Silicon photonics have been used in an increasing variety of applications, including waveguides, modulators, resonators, and lasers. In many of these applications, the functioning of the silicon photonic devices may depend on the index of refraction of the silicon. However, the index of refraction of silicon varies with temperature due to the thermo-optic effect, and the amount that the index of refraction varies with temperature is called the thermo-optic coefficient (“TOC”). Since many silicon photonic devices may be used in environments that have temperature variations during their operation, the TOC of silicon may result in the optical properties of silicon photonic devices varying with temperature to an extent that their operation is adversely impacted.
Active temperature stabilization techniques to control the temperature of silicon photonic devices have been used to limit the temperature variation and thus reduce the impact of the TOC of silicon on the functioning of many of these devices. However, active temperature stabilization may be difficult to implement for some devices, and if implemented may be energy-inefficient.
Passive compensation for the TOC of silicon has been implemented using polymer cladding materials such as Poly-Methyl-Meth-Acrylate (PMMA) with a negative TOC to compensate for the positive TOC of the silicon in some photonic devices. However, such polymer materials may not be compatible with the processes typically used in the fabrication of complementary metal-oxide semiconductor (CMOS) devices, and therefore these polymers may not be able to be readily incorporated into existing CMOS fabrication processes. Additionally, these polymers may absorb water, become chemically unstable, be mechanically weak, and/or undergo photo-degradation and, therefore, may often be undesirable for use in silicon photonic devices.